Android 网络图片查看器

由于android下的网络连接不能在主线程操作，另外UI的改变也只能通过主线程来变化，所以一般来说操作网络我们都要开启一个子线程执行，而UI的改变则通过handler消息传递给主线程，委托主线程操作。

以下是一个android网络图片查看器，需要传入一个URL地址来查看该图片：

package com.wuyou.webimgbrowser;


import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.support.v7.app.ActionBarActivity;
import android.text.TextUtils;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.Toast;

import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;

public class MainActivity extends ActionBarActivity {

    //常量：改变显示的图片
    private static final int CHANGE_IMG = 1;
    private static final int ERROR = 2;

    private ImageView imageView;
    private EditText editText;
    private Button button;

    //消息处理器
    private Handler handler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            if (msg.what == CHANGE_IMG) {
                Bitmap bitmap = (Bitmap) msg.obj;
                imageView.setImageBitmap(bitmap);
            } else if (msg.what == ERROR) {
                Toast.makeText(MainActivity.this, "获取图片失败！", Toast.LENGTH_LONG).show();
            }
        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        imageView = (ImageView) findViewById(R.id.iv);
        editText = (EditText) findViewById(R.id.et);
        button = (Button) findViewById(R.id.bt);

    }

    public void click(View view) {
        final String path = editText.getText().toString().trim();

        //子线程不能修改UI，只能通过消息发送到主线程，让主线程代替修改UI
        new Thread(new Runnable() {
            @Override
            public void run() {
                if (TextUtils.isEmpty(path)) {
                    sendError(null);
                } else {
                    try {
                        System.out.println("path = " + path);
                        URL url = new URL(path);
                        HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
                        httpURLConnection.setRequestMethod("GET");//设置以get方式获取资源
                        httpURLConnection.setConnectTimeout(5000);//设置连接服务器如果没有在5秒钟运行则抛出错误
                        httpURLConnection.setRequestProperty("User-Agent", "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:22.0) Gecko/20100101 Firefox/22.0");
                        if (httpURLConnection.getResponseCode() == 200) {
                            InputStream inputStream = httpURLConnection.getInputStream();
                            Bitmap bitmap = BitmapFactory.decodeStream(inputStream);
                            Message message = new Message();
                            message.what = CHANGE_IMG;
                            message.obj = bitmap;
                            handler.sendMessage(message);
                        } else {
                            sendError(null);
                        }
                    } catch (Exception e) {
                        sendError(e);
                    }
                }
            }

            //发送错误
            private void sendError(Exception e) {
                if (e != null) {
                    e.printStackTrace();
                }
                Message message = new Message();
                message.what = ERROR;
                handler.sendMessage(message);
            }
        }).start();
    }


}

其中布局文件：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity"
    android:orientation="vertical"
    tools:ignore="MergeRootFrame">

    <ImageView
        android:id="@+id/iv"
        android:layout_weight="3000"
        android:layout_height="match_parent"
        android:layout_width="match_parent" />

    <EditText
        android:text="http://image.sjrjy.com/201011/291354164ea84578066309.jpg"
        android:lines="1"
        android:id="@+id/et"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content" />

    <Button
        android:id="@+id/bt"
        android:text="浏览图片"
        android:onClick="click"
        android:layout_height="wrap_content"
        android:layout_width="wrap_content" />

</LinearLayout>

最后不要忘了在清单文件添加：（网络连接的权限）

<uses-permission android:name="android.permission.INTERNET" />